The present disclosure relates to compositions and methods for treating subterranean formations, and more specifically, for the treatment of siliceous materials (e.g., silica and/or other silicates) in subterranean applications.
Drilling and servicing fluids may be used to produce hydrocarbon formations penetrated by well bores. The drilling fluids may be utilized when well bores are drilled into producing or injecting formations to minimize damage to the permeability of the formations and their ability to produce hydrocarbons and or accept injected fluids or gas. Servicing fluids may be utilized when completion operations are conducted in formations and when conducting work-over operations in the formations. The drilling and servicing fluids may deposit filter cake on the walls of the well bore within a formation, which may prevent the drilling and servicing fluids from being lost into the formation and may prevent solids from entering the porosities of the formation. Since the filter cake often reduces the permeability of a formation and obstructs the flow of fluid, the filter cake may be removed prior to placing the formation on production or injection. The removal of the filter cake may be accomplished by including an acid soluble bridging agent in the drilling or servicing fluid for bridging over the formation pores. The filter cake formed by the drilling or servicing fluid, which may include the bridging agent and a polymeric suspending agent, may be contacted with a strongly acidic solution, and the acidic solution may be allowed to remain in contact with the filter cake for a period of time sufficient to degrade the filter cake.
Hydrocarbon-bearing portions of subterranean formations penetrated by well bores also may be treated to stimulate the production of hydrocarbons therefrom. One such treatment, generally referred to as “acidizing,” involves the introduction of an aqueous acid solution into a subterranean formation under pressure so that the acid solution flows through the pore spaces of the formation. The acid reacts with and/or dissolves acid soluble materials contained in the formation thereby increasing the size of the pore spaces, thus increasing the porosity and/or permeability of the formation. Another production stimulation treatment known as “fracture-acidizing” comprises injecting a treatment fluid comprising an acid into the formation at a pressure sufficient to create or enhance one or more fractures within the subterranean formation. The acid treatment fluid may leave one or more voids within the formation in addition to the one or more fractures enhanced within the formation. Another method of acidizing, known as “matrix acidizing,” comprises injecting the treatment fluid into the formation at a pressure below that which would create or enhance one or more fractures within the subterranean formation. This acidizing method may likewise leave one or more voids within the formation.
Filter cakes and formations to be acidized (e.g., sandstone formations) often comprise some amount of silica or silicates, including but not limited to silica gels, colloidal silica, feldspars, and/or quartz. In order to remove filter cakes and/or to effectively acidize formations containing these species, the silica and/or silicates must be at least partially dissolved. Conventional techniques often involve using fluorides such as hydrofluoric acid (HF) or acid salts (e.g., ammonium bifluoride) to dissolve such silica or silicates. However, these fluorides may have undesirable environmental and/or toxicity problems, and as such may be impractical to use or prohibited altogether in certain circumstances and/or jurisdictions. Hydrofluoric acid and other fluorides also may pose undesirable health and/or safety risks to personnel working at a site where they are used. Moreover, strongly acidic solutions of HF may corrode metallic surfaces and completion equipment (e.g., sand screens), leading to their early failure.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.